Electromagnetic coils



Dec. 29, 1964 A. zAcK ELECTROMAGNETIC cons Original Filed Dec. 30, 1953FIG.3

FIG. 4

AL BERT 2 AC K INVENTOR.

ATTORNEY United States Patent 3,163,839 ELECTRGMAGNETIC COILS AlbertZach, Danvers, Mass, assignor, by mcsne assignments, to SylvaniaElectric Products Inc, Wilmington, Dick, in corporation of DelawareOriginal application Dec. 30, W53, Ser. No. 401,333, now Patent No.3,113,374, dated Dec. 10, 1963. Divided and this application Jan. 3,1961, Ser. No. 93,826

2 Claims. (Cl. 336-192) This invention relates to coils, particularlyfor electrical purposes, in which the turns of the coil are ordinarilyspaced apart by an insulating material, and to the manufacture of suchcoils.

This application is a divisional of copending application Serial No.401,333, now Patent No. 3,113,374, filed December 30, 1953, in the nameof Albert Zack.

Such coils are ordinarily made by winding wire of round cross-section inwide layers on a core. The round Wire gives a poor space factor, yet theuse of wire of rectangular cross-section is not feasible on automaticmachinery because of the difficulties due to twisting of the wire, whichis especially diflicult if the wire is extremely fine.

I have discovered, however, that very effective coils can be made bywinding wide foil sheets in layers separated by an insulating material,for example a sheet of paper, and then slicing the resultant piece intothin wafers, each of which will be in effect a spiral coil ofrectangular wire, the turns of which are separated by the insulatingmaterial.

These spiral coils can be impregnated with wax, resin, plastic or otherinsulating materials before slicing, and can be used directly, as in ahigh frequency coil, or enclosed partly or wholly in magnetic material,or placed on a magnetic core. The spirals can be stacked together,separated from one another by a thin wafer of insulating material or byan insulating film, with the spirals being connected in series if alarge number of turns is desired, with some of the coils acting asprimaries, the others as secondaries if the resultant device is to be atransformer. One spiral can be a primary, the next a secondary, and

so on if tight coupling is desired, or all the primary spirals can betogether, and all the secondaries together, if looser coupling iswanted.

In slicing the wound layers into coils, the turns may become shorted,but the shorts can be removed by etching in an acid which dissolves themetal, the etching being continued long enough to dissolve out theshorted metal but not long enough to remove much of the unshorted metalin the interstices of the coil. However, I have found that if thecutting tool is extremely thin and sharp, and if its rate of progressinto the coil is kept at a critical value with respect to the rotationof the wound piece,

the slicing operation can be carried out without producing any short,and hence without the necessity of etching.

The coils produced are superior to conventional wirewound coils becauseof the thinner insulation which can be used between layers, therectangular cross-section of the conductors, and the thinness of theconducting material. The manufacturing cost of the coils is, moreover,much smaller than that for conventional coils of similarcharacteristics' and the manufacture is more readily adaptable tocompletely automatic machinery.

Other features, advantages and objects of the invention will be apparentfrom the following specification, taken in connection with theaccompanying drawing, in which:

FIG. 1 shows a sheet of metal foil and a sheet of paper being wound on acore together;

FIG. 2 shows the wound cylinder being sliced into Wafers;

3,163,839 Fatented Dec. 29, 1964 "Ice PEG. 3 shows a resultant singlewafer-like coil; and FIG. 4 shows in radial cross-section a means ofconmeeting the wafer-like spiral coils.

In FIG. 1, a cylindrical core 1, which may for example be of wood, isrotated to wind thereon the paper sheet 2 and the metal foil sheet 3,the direction of rotation being shown by the arrow. The sheets 2 and 3can be unwound from separate spools, 4, 5 and Wound together on the core1, by rotating the latter, which may be set in a chuck for that purpose.The rolls 12, 13 of paper and foil, re-

spectively, can turn about the shafts 4, 5, which may be fixed. Thepaper used can be paper of the insulating type used in condensers,generally called kraft paper, and can have a thickness, for example, assmall as 0.0003 inch or even less. The foil is also thin, about 0.00025inch; aluminum foil being satisfactory for many purposes. The gains fromthe method of Winding are such that when aluminum foil is used, theresistance of the finished coil is about the same as that obtained byusing copper in the conventional wire windings. When copper is used withthe wafer-coils described in the present application, the coilcharacteristics are far superior to those of wirewound coils. Copperfoil, however, is not generally obtainable in sizes as thin as thethinnest aluminum foil. Where aluminum foil is used as the conductor, alength of copper foil is generally used in overlap contact to thealuminum foil 16 at the ends of the latter, to facilitate soldering theconnections. If the copper foil overlaps the aluminum for several turns,a firmer joint between the copper and aluminum is provided.

The wound cylinder 6 is then impregnated with Wax, by being set into acontainer of melted wax for about 24 hours in air, then for about 48hours in vacuum. It is then allowed to dry.

The wax is preferably one whose melting point is above the temperatureto which the coil is brought by the friction of slicing. Waxes meltingat 240 F. have been found satisfactory, and they can be heated to 275 F.during impregnation. Various resins and plastics can be used instead ofwax, for example polyethylene, polystyrene, and polyvinyl plastics. Inaddition to its insulating effect the impregnation holds the woundcylinder 6 together and keeps it from unravelling.

When the coil is wound to the desired size on the cylinder andimpregnated, the resultant wound cylinder 6 is then sliced into wafers 7with the razor blade 8, which may be mounted on a metal arm 9, attachedto a toolholder in a lathe, the wound cylinder 6 being set into thechuck of the same lathe and in position to be cut by the tool, whichshould be set at right angles to the longitudinal axis of the cylinder6. In one example, the cylinder 6 was 3 inches long, and was cut intowafers about 0.013 inch long.

For best results in cutting the wound cylinder 6 into wafers 7 withoutshorted turns, the lathe cross-feed should not be advanced, for eachrevolution of the wound cylinder 6, more than a distance equal to thecombined thickness of one sheet of foil plus one sheet of paper, thatis, the radial distance between the center line of two adjacent turns offoil.

As shown in FIG. 3, each resultant wafer-coil 7 will have one contact 1%at its inner end and one It at its outer end. The core 1 is shownremoved in the coil of this figure. If the coils A, B, shown in radialcross-section in FIG. 4 are stacked so that their windings are all inthe same direction, the inside contact 10 of one will be connected tothe outside contact 11 of the next, if they are desired to be connectedin series-aiding relationship. However, if alternate coils A, B, arereversed so that their windings are in opposite directions, for example,so the winding of A is clockwise and of B counter-clockwise, then thecoils can be connected together by connecting the inner metal contactterminals 10, of one pair of coils together, through the wire 14, theouter metal contact terminals 11, 11 of the next pair together, throughthe wire and so forth, the two metal terminals 11, 11 at the outsideends of the stack of coils being left free for connection to an externalcircuit.

Coils connected in the foregoing manner would of a plastic insulatingcoating is used over one side of the foil surface. desired.

The foil can be insulated before winding, if desired, by spraying with athin layer of glass or ceramic frit, the coil being heated suflicientlyafter Winding to melt the foil and seal the unit together. Although arazor-blade type cutter is very effective, a rotataingwheel cutter canalso be used, the wheel being driven in a direction opposite to that ofthe rotation of the wound cylinder 6.

The foil used is too thin to form of itself spaced turns which areself-supporting, but when wound as described herein with paper or otherinsulating material between turns, the resultant unit is completelyself-supporting.

Instead of connecting the coils A, B in FIGURE 4 to gether by wires 14,15, they can be connected by twisting the terminals 10, 10 or 11, 11together.

Wound paper can be used for the core if What I claim is:

1. A spiral electromagnetic coil comprising a spiral of thin aluminumfoil With a thin layer of solid insulating material between the turns ofthe coil and spacing said turns apart, and a short length of thin copperfoil overlapping an end portion of the aluminum foil near the outercircumference of the coil and in direct close contact therewith to actas a terminal contact for said aluminum foil.

2. A spiral electromagnetic coil comprising a spiral of turns of thinaluminum foil with a thin layer of solid insulating material between theturns of the coil and spacing said turns apart, and a short length ofthin copper foil overlapping several turns of the spiral at an endportion of the aluminum foil and in close direct contact therewith toact as a terminal contact for said aluminum foil.

References Cited by the Examiner UNITED STATES PATENTS 734,778 7/03Varley 336-223 1,573,852 2/26 OLeary 336-223 X 2,192,751 3/40 Melchoiret a1. 339-278 2,389,640 11/45 Ruben 336-233 X 2,513,365 7/50 Rozoff339-278 2,521,513 9/50 Gray 336-223 X 2,550,592 4/51 Pearce 336-223 XJOHN F. BURNS, Primary Examiner.

MILTON O. HIRSHFIELD, Examiner.

1. A SPIRAL ELECTROMAGNETIC COIL COMPRISING A SPIRAL OF THIN ALUMINUMFOIL WITH A THIN LAYER OF SOLID INSULATING MATERIAL BETWEEN THE TURNS OFTHE COIL AND SPACING SAID TURNS APART, AND A SHORT LENGTH OF THIN COPPERFOIL OVERLAPPING AN END PORTION OF THE ALUMINUM FOIL NEAR THE OUTERCIRCUMFERENCE OF THE COIL AND IN DIRECT CLOSE CONTACT THEREWITH TO ACTAS A TERMINAL CONTACT FOR SAID ALUMINUM FOIL.